Gypsum plaster board



Jan.' 2'4, 1967 l H. E. HAR-f 3,300,371

GYPSUM PLJASTER BOARD 'Filed D60. ll 1961 United States Patent O3,300,371 GYPSUM PLASTER BOARD Harry E. Hart, Hinsdale, Ill., assignorto The Celotex Corporation, a corporation of Delaware Filed Dec. 11,1961, Ser. No. 158,411 8 Claims. (Cl. IGI- 229) The present inventionpertains to a gypsum core plaster board which can be used conventionallyas wallboard or as a plaster base, and more particularly to an improvedgypsum plaster board to which plaster or a water base paint may beadhered.

It is customary in finishing the interior walls and oeilings of abuilding to provide a plaster surf-ace which is applied to a backing. Apreferable type of backing is a -gypsum plaster board or gypsum lathcomprising a core of set gypsum and paper cover sheets enclosing thecore. A major problem in the use of such paper covered sheets is theprovision of rapid and uniform water absorption from the plaster appliedto the surface thereof. Without such rapid and uniform water absorptionthere is a lowering of the strength in the plaster facing. Furthermore,rapid and uniform water absorption is necessary t-o lreduce slippage ofthe plaster on the wall when it is rodded or darbied.

Another factor of great importance is the strength of the bond betweenthe gypsum core and the paper cover sheets, so that the paper coversheets will not peel or delaminate from the ygypsum core. A weakness ofthe interface bond may produce a totally unacceptable wall iinish.Additionally, it is necessary that the paper cover sheets, which :areconventionally manufactured, do not delaminate between their adjacentplies.

With reference to the paper cover sheets themselves, they must be ofuniform strength throughout with strong bonds between the plies.Additional wet and dry strength in the paper cover sheets make itpossible t-o reduce the caliper or thickness of the sheets, thusreducing the lweight of the paper used. A reduced weight is `reflectedin a reduced freight rate and a cost `savings on the paper stock broughtto the gypsum board plant.

Also, increased strength in the paper cover sheets with a reduction inits thickness vastly improves t-he scoring properties of the gypsum lathas well as improving its nailing characteristics.

There is presently available a type of lath in which at least one ply ofthe paper cover sheet incorporates ta urea or melamine type resin tosupplement the conventional rosin and alum size. However, thisadditional resin which is compatible with the rosin and alum size doesnot preh vent the migration of the size in the cover sheet to theinterface between the gypsum core and the cover sheet. At times thepresence of the size at the surface of the gypsum core produces a slickbond, which means the crystals of gypsum at the interface do notpenetrate the paper cover sheets and the paper to gypsum bond is greatlyimpaired.

It is, therefore, an object of the present invention to provide a gypsumboard which has uniform and rapid water absorption over its surface.

It is yet another object of the present invention to provide a novelgypsum board or lath in which the strength of the Wet bond between theplies of the paper and the bond between the paper cover sheets and thegypsum core is greatly improved.

It is a further object of the present invention to provide a novelgypsum board in which the paper is of reduced caliper compared to moreconventional board paper and thus, lighter in weight.

These and other objects and advantages of the present invention willbecome more apparent when the following more detailed description of theinvention is considered with the accompanying drawing, and in which:

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The drawing is a cross-sectional view of the plaster 'board of thepresent invention.

Referring now to the drawing, there i-s therein shown a plaster board orlath 10 comprising a gypsum core 11 and facing sheets 15 and 16. Each ofthe facing sheets 15 and 16 is made up of seven plies 1824 and 27-33,respectively. Of course, it should be understood that since only oneside of the plaster lath will ordinarily receive a plaster coat, onlyone of the sheets 15 tand 16 need be used. In this latter case, theother sheet may be of such conventional paper as is now available.

The core 11 is conventional and comprises the usual ingredients of a setslurry of calcium sulfate hemihyd-rate, water, starch, foam, etc. Thespecific process for making gypsum plaster board is well known, and forthis reason a detailed explanation of this process will not be repeated.

The paper cover sheets 15 and 16 are bonded to the core 11 by thepenetration of gypsum crystals which, when the excess water of thegypsum slurry is driven ot by drying, interlock with the paper fibers inthe sheet t-o form a stable and a strong bond. As indicated, the papercover sheet 15 is made with seven plies. This paper can be made on anyconventional cylinder paper making machine having seven wells orcompartments for holding the paper stock individually for each ply. Thethree innermost plies 20, 21 and 22, are made with conventional paperfiber stock that has been sized. In refining t-he paper stock for allthe plies ground wood, sulfate or sulphite stock should be used.

The two plies 19 and 23, lying immediately outside of the three centralplies 20-22, are made lwithout any sizing at all, but contain analkaline salt or alkaloid t-o -act as a buffer and prevent migration ofthe size from the central plies. As will become more .apparent later,this buffer zone is of extreme importance in :achieving the novel lathof the invention. While many suitable alkaline salts and alkalies may beused, soda ash -or caustic soda have been found -to be preferable. Anorganic alkaloid may be used, if desired.

The two outermost plies 18 and 24 contain a polyamide resin which 4iscompatible with ian alkaline pH. Preferably, the pH of the stock in theouter plies is held at a pH of 7.10, or higher. The pH may be maintainedby adding sui-licient -alkaline salts or alkaloid compounds. The resinis added to the furnish in the cylinder wells in an amount of about 0.1to 5.5%. Resin in an amount of 5.5% has been added `to the furnish, butexperiments indicate that more resin may be added without imparing thedesired characteristics of the paper. The wet strength of the paper willvary depending upon the amount of resin added.

While the specific example has referred to a cylinder machine :havingseven wells, other paper making machines may be used. Thus, theinverformer, which does not use Wells, may be used with equaleffectiveness.

Also, the resin and other ingredients may be added to the furnish atplaces other than the wells. For example, the ingredients may be addedto the paper stock at the head box or Jordans.

Furthermore, while a seven ply paper has been found to be practical, thenumber of plies may be reduced to as low as three. In this latter case,the center ply contains the alkaline buffer and the two outer pliescontain the polyamide resin.

The specific resin added to the outermost plies is an uncuredthermosettng cationic resin comprising a water soluble polymericreaction product of epichlorohydrin and a polyamide derived from apolyalkylene polyamine and a saturated aliphatic diba-sic carboxylicacid containing about 3 to 10 carbon atoms. Such a resin is commerciallyavailable from the Hercules Powder Company of Wilmington, Delaware, andsold under the trade name of Kymene 557. Additionally, completeinformation as to the characteristics of the resin and its manner ofmanufacture may be found in U.S. Patent No. 2,926,154, issued to GeraldI. Keim on February 23, 1960. Further information with regard to the useof this resin in the production of a wet strength sheet may be found inU.S. Patent No. 2,926,116, issued to Gerald I. Keim, on February 23,1960.

The actual manufacture of the gypsum lath, as previously indicated, isconventional. A proper gypsum slurry with calcium sulfate hemihydrate,water starch, foam, accelerator, etc., is made and dropped on a papercover sheet in a conventional gypsum wallboard machine. The paper sheetis folded so that its outer edges are slightly retroverted and arespaced inwardly from the edge of the lath. A top cover sheet is appliedto the upper exposed surface of the gypsum slurry and glued to theretroverted edges of the bottom sheet. The sandwich of gypsum core withits enclosing paper cover sheets is conveyed on a belt until the gypsumcore sets. After this, the sandwich is cut to appropriate length and isconveyed through a drier where the excess water is driven from thegypsum core after final set takes place.

In comparing the gypsum lath of the invention made with the novel paper,with more conventional gypsum lath, there has been found to be anunusually strong bonding between the plies of the paper and between thegypsum core and the paper. The fact that the sizing agent is confined tothe three interior plies and not permitted to migrate through thealkaline barrier ply avoids the danger of a poor bond between the paperand the gypsum core. A comparison has been made between conventionalgypsum lath and the novel gypsum lath of the invention lby wetting thepaper and then abrading the moisture laden paper. In the case of regulargypsum lath, the paper was found to delaminate in separate plies. Incontrast to this, the novel paper of the invention did not laminate butthe plies were strongly bonded together.

A test was made of the nature of the water absorption of conventionalgypsum lath and the novel lath of the present invention. In this test, asmall glass holding one ounce of water was inverted on the surface ofeach type of lath. In the case of conventional lath, the water spreadover an area about twice the area of the spread of the water on thesurface of the novel lath. Thus, indicating that the actual waterabsorption of the novel lath was about twice that of conventional gypsumlath. This characteristic of enhanced water absorption results in agreater density and higher strength of the plaster applied to thesurface of the novel gypsum lath of the invention.

With regard to the paper itself, it has been found advan-I tageous tomake it in a balanced condition. By balanced condition is meant thatthere is a plane of symmetry within the paper at the center runningparallel to the surface of the paper. Thus, the center ply 21 is sizedwith rosin and alum, the next plies 20 and 22 adjacent to the center ineach direction from the center ply 21 is also sized with rosin and alum,the next plies 19 and 23 outwardly of plies 20 and 22 contain analkaline or alkaloid buer system and the two outermost plies 18 -and 24contain the cationic polyamide resin. In this way, there is uniformstrength throughout the paper.

As indicated, the resin employed in the outer plies 18 and 24 iscationic in nature. It has been found that anions in the ply next to thegypsum core prevent proper crystalline formation at the interface of thegypsum core and the paper. The use of a cationic resin obviates thiscondition and a stronger bond between the gypsum core andthe paperresults. In summary, there has been disclosed a novel plaster lathhaving rapid and uniform water absorption, lighter in weight andproducing a strong bond !between the plies of the paper and also betweenthe paper cover sheets and the gypsum core than has heretofore beenavailable.

While there has been shown the best known mode of the invention, otherchanges and modifications may be made by those skilled in the art, andit is intended to cover such changes and modifications in the appendedclaims.

I claim:

1. A plaster base for receiving a face coat of plaster comprising a setgypsum core, cover sheets bonded to exposed faces of said core, each ofsaid cover sheets being of multiple ply construction having at least onecentral ply, said central ply being sized with sufiicient rosin and alumsize to prevent tearing of the paper under tension; two plies outwardlyadjacent to said central ply having an alkaline buffer therein in aneffective amount to prevent migration of the rosin size beyond said twobuffer plies, and two additional plies outwardly adjacent to said bufferplies, said outermost plies of each sheet containing a cationicpolyamide resin dispersed therein.

2. A plaster base for receiving a face coat of plaster as recited inclaim 1, in which said cationic polyamide resin is in an amount of atleast 0.1% lby weight of said paper sheet.

3. A paper sheet for lamination to a gypsum core cornprising multipleplies, said paper having at least one central ply, said central plybeing sized with suflicient rosin and alum size to prevent tearing ofthe paper under tension; two plies outwardly adjacent to said centralply having an alkaline buffer therein in an effective amount to preventmigration of the rosin size beyond said two buffer plies, and twoadditional plies outwardly adjacent to said buffer plies, said outermostplies of each sheet containing a cationic polyamide resin dispersedtherein.

4. A paper sheet for lamination to a gypsum core as recited in claim 3,in which said cationic polyamide resin is in an amount at least 0.1% byweight of said paper sheet.

5. A plaster base for receiving a face coat of plaster comprising a setgypsum core, cover sheets bonded to exposed faces of said core, each ofsaid cover sheets being of multiple ply construction having at least onecentral ply, said central ply being sized with sufficient rosin and alumsize to prevent tearing of the paper under tension; two plies outwardlyadjacent to said central ply having an alkaline buffer therein in aneffective amount to prevent migration of the rosin size beyond said twobuffer plies, and two additional plies outwardly adjacent to said bufferplies, said outermost plies of each sheet containing a cationicpolyamide resin dispersed therein, said cationic polyamide resincomprising a water soluble polymeric reaction product of epichlorohydrinand a polyamide derived from a polyalkylene polyamine and a saturateddibasic carboxylic acid containing about 3 to 10 carbon atoms dispersedtherein.

6. A paper sheet for lamination to a gypsum core comprising multipleplies, said paper having at least one central ply, said central plybeing sized with suflicient rosin and alum size to prevent tearing ofthe paper under tension; two plies outwardly adjacent to said centralply having an alkaline buffer therein in an effective amount to preventmigration of the rosin size beyond said two buffer plies, and twoadditional plies outwardly adjacent to said buffer plies, said outermostplies of each sheet containing a cationic polyamide resin dispersedtherein, said cationic polyamide resin comprising a water solublepolymeric reaction product of epichlorohydrin and a polyamide derivedfrom a polyalkene polyamine and a saturated dibasic carboxylic acidcontaining about 3 to 10 carbon atoms dispersed therein.

'7. A plaster board comprising a set gypsum core, cover sheets bonded toexposed faces of said core, each of said cover sheets being of multipleply construction having at least one central ply, said central ply beingsized with suicient rosin and alum size to prevent tearing of the paperunder tension; two plies outwardly adjacent to said central ply havingan alkaline buffer therein in an effective amount to prevent migrationof the rosin size beyond said two buffer plies, and two additional pliesoutwardly adjacent to said butler plies, said outermost plies of eachsheet containing at least 0.1% of a cationic polyamide resin dispersedtherein.

8. A paper sheet for lamination to a gypsum core comprising multipleplies, said paper having at least one central ply, said central plybeing sized with suflicient resin and alum size to prevent tearing ofthe paper under tension; two plies outwardly adjacent to said centralply having an alkaline buffer therein in an elective amount to preventmigration of the rosin size beyond said two buffer plies, and twoadditional plies outwardly adjacent to said buffer plies, said outermostplies of each sheet containing at least 0.1% of a cationic polyamideresin dispersed 15 therein.

References Cited by the Examiner UNITED STATES PATENTS 2,226,553 12/1940 Cross.

2,344,600 3/ 1944 Codwise 161-246 2,562,859 7/ 1951 Camp 161-2702,806,811 9/ 1957 Von Hazmburg 161-246 FOREIGN PATENTS 1,102,628 3/ 1961Germany.

ALEXANDER WYMAN, Primary Examiner.

EARL M. BERGERT, Examiner.

R. J. ROCHE, Assistant Examiner.

1. A PLASTER BASE FOR RECEIVING A FACE COAT OF PLASTER COMPRISING A SETGYPSUM CORE, COVER SHEETS BONDED TO EXPOSED FACES OF SAID CORE, EACH OFSAID COVER SHEETS BEING OF MULTIPLE PLY CONSTRUCTION HAVING AT LEAST ONECENTRAL PLY, SAID CENTRAL PLY BEING SIZED WITH SUFFICIENT ROSIN AND ALUMSIZE TO PREVENT TEARING OF THE PAPER UNDER TENSION; TWO PLIES OUTWARDLYADJACENT TO SAID CENTRAL PLY HAVING AN ALKALINE BUFFER THEREIN IN ANEFFECTIVE AMOUNT TO PREVENT MIGRATION OF THE ROSIN SIZE BEYOND SAID TWOBUFFER PLIES, AND TWO ADDITIONAL PLIES OUTWARDLY ADJACENT TO SAID BUFFERPLIES, SAID OUTERMOST PLIES OF EACH SHEET CONTAINING A CATIONICPOLYAMIDE RESIN DISPERSED THEREIN.